1. Technical Field
The present disclosure relates to an illumination device. More particularly, the present disclosure relates to an illumination driving circuit on an illumination device.
2. Description of Related Art
With the rapid development of photoelectric technology in recent years, the industry has developed many kinds of innovative illumination equipments including light-emitting diode (LED) lamps, which are widespread and gather high attentions. Luminous efficiency and durability of the LED lamps are superior to traditional incandescent tubes. In addition, the LED lamps may not cause environmental issues in manufacturing, such that the LED lamps are welcome in the trend of energy saving and environmental protection.
The frequently mentioned advantages of a lighting system composed of LED lamps include high efficiency and long durability. The conversion efficiency and the power factor (PF) are two main factors to achieve the high efficiency on the LED lamps.
Conversion efficiency is referred to how much input power is actually passed to the LED, during the process from the alternating-current (AC) power input to the LED output. The conversion efficiency is higher when a higher proportion of the input power is communicated to the output power.
The power factor is related to the real power and the reactive power within a power signal. The power company provides a three-phased AC power signal with a household voltage ranged from 100V˜110V or 200V˜240V and an alternating frequency ranged from 50 Hz˜60 Hz. In general, an instantaneous consumption power of a resistive load is the product of voltage and current (i.e., P=VI). However, a pure inductive load or a pure capacitive load may cause a phase difference of 90° between current and voltage, and the phase difference will result in a loss of real power. The instantaneous consumption power can be calculated as follows:
P=VI cos θ, in which I represents the current, V represents the voltage, and θ represents the phase difference between the current and the voltage.
In addition, the power factor can be calculated as follows:
      PF    =                  VI        ⁢                                  ⁢        cos        ⁢                                  ⁢        θ            VI        ,in which PF represents the power factor, I represents the current, V represents the voltage, and θ represents the phase difference between the current and the voltage.
As shown in the expression above, when the phase difference between current and voltage is 90° (e.g., when the load is a pure inductive load or a pure capacitive load), the power factor will be substantially decreased to zero.
Because LED is not a pure resistive load and the driving circuit for driving LED may bring in the characteristics of inductance and capacitance, it will result in the phase difference between the input voltage and the input current, and also result in the declination of the power factor. In this case, the power company must provide more power output for driving the LED to reach its predetermined output power. The reactive power caused by the phase difference may be converted into unnecessary heat consumption. Therefore, the improvement of the power factor may contribute to reduce the requirement of the output power from the power company, so as to save electricity in practical applications.
Therefore, in order to achieve the goal of energy-saving, it is necessary to develop the LED illumination equipment with high power factor.